class Solution:
    def pivotIndex(self, nums: List[int]) -> int:

        totalSum = sum(nums)
        running_sum = 0

        for i in range(len(nums)):
            running_sum = running_sum + nums[i]

            left_sum = running_sum - nums[i]
            right_sum = totalSum - running_sum

            if left_sum == right_sum:
                return i

        return -1